The goal of the proposed project is to conduct a large-scale effectiveness trial that will test whether a brief group cognitive-behavioral (CBT) depression prevention program, which has produced significant reductions in depressive symptoms and reduced risk for onset of future depressive episodes in preliminary efficacy trials, produces intervention effects when school personnel are responsible for screening, recruitment, and delivery of this selective prevention program. In contrast to efficacy trials, where researchers have substantial control over intervention implementation with homogeneous samples, effectiveness trials examine the effects of interventions that are delivered by endogenous providers to heterogeneous samples in natural settings (e.g., schools). The secondary aim is to test whether a CBT-based self-help book (CBT bibliotherapy) also produces positive intervention effects, as was observed in two preliminary trials. It seemed particularly important to investigate bibliotherapy within an effectiveness trial because it would be much less expensive and easier to disseminate to large numbers of adolescents than a group-based intervention. We believe that the proposed study would be the first large-scale evaluation of CBT bibliotherapy for the prevention of adolescent depression. Over a 3-year period, 390 high school adolescents at risk for depression due to elevated depressive symptoms will be randomized to (1) a 6-session group CBT intervention, (2) CBT bibliotherapy, or (3) a monitored control condition. Participants will complete surveys and diagnostic interviews at pre, post, and 6, 12, 18, and 24-month follow-ups. We hypothesize that participants in the group CBT and CBT bibliotherapy conditions will show significantly greater reductions in depressive symptoms and reduced risk for onset of major depression than controls through follow-up, but expect significantly larger effect sizes for group CBT relative to CBT bibliotherapy for many outcomes, as observed in our largest preliminary study. We will also test whether decreases in negative cognitions and negative attributional style, increases in pleasant activities, knowledge of CBT principles, and use of cognitive and behavioral coping skills mediate any effects of the interventions on depression outcomes. Further, we will examine moderators that potentiate (verbal intelligence, coping skills, motivation) or mitigate (negative life events, social support deficits) intervention effects. Analyses will test whether, relative to monitored controls, participants in either of the CBT interventions show improvements in ecologically meaningful outcomes, including psychosocial functioning, days of school or work missed because of mental health problems, substance use/abuse, or mental health care utilization over the 2- year follow-up. We specifically hypothesize that group CBT will show significantly greater improvements on the broadest array of outcomes. Public Health Relevance: This project would be the first large-scale trial of two empirically supported depression prevention programs for high-risk adolescents in real-world settings. As such, it will provide vital information necessary for disseminating the most effective and cost efficient methods of preventing this pernicious condition, which is crucial because no depression prevention program has been widely disseminated.